Shifting focus to the Aviary 1.0 branch as of this post. The bug list has been tidied up in preparation for the 0.8 release of Thunderbird. (Draft Release Notes, post your feedback)
Bugs targeted for 0.8 are here.
– Those no longer listed above may still be present as a regression, but may no longer be in development.
– These currently listed above may be blocking Aviary 1.0 (or its sub-branches), or are blocker bugs.

CSS style sheets will be implemented… EDIT: Done!

Important note from Scott MacGregor over at Mozillazine Forums which applies as of this build:
“The version string has been bumped to 0.8 to help test out the new extension manager changes. Any extensions that aren’t listed on update.mozilla.org as being compatible with 0.8 will get disabled upon first launch.”